Tyrosine kinase receptors are trans-membrane proteins that, in response to an extracellular stimulus, propagate a signaling cascade to control cell proliferation, angiogenesis, apoptosis and other important features of cell growth. One class of such receptors, epidermal growth factor receptor (EGFR) tyrosine kinases, are overly expressed in many human cancers, including brain, lung, liver, bladder, breast, head and neck, esophagus, gastrointestinal, breast, ovary, cervix or thyroid cancer.
EGFR is expressed in many types of tumor cells. Binding of cognate ligands (including EGF, TGFα (i.e., Transforming Growth Factor-α) and neuregulins) to the extracellular domain causes homo- or heterodimerization between family members. The juxtaposition of cytoplasmic tyrosine kinase domains results in transphosphorylation of specific tyrosine, serine and threonine residues within each cytoplasmic domain. The formed phosphotyrosines act as docking sites for various adaptor molecules and subsequent activation of signal transduction cascades (Ras/mitogen-activated, PI3K/Akt and Jak/STAT) that trigger proliferative cellular responses.
Various molecular and cellular biology and clinical studies have demonstrated that EGFR tyrosine kinase inhibitors can block cancer cell proliferation, metastasis and other EGFR-related signal transduction responses to achieve clinical anti-tumor therapeutic effects. Two oral EGFR kinase inhibitors with similar chemical structures are Gefitinib (Iressa, AstraZeneca), approved by the U.S. FDA for advanced non-small cell lung cancer in 2003 (and later withdrawn), and Erlotinib Hydrochloride (Tarceva, Roche and OSI), approved by the U.S. FDA for advanced non-small cell lung cancer and pancreatic cancer treatment in 2004.
Many pharmaceutically active organic compounds can crystallize in more than one type of three-dimensional crystal structure. That is, the compounds may crystallize in different crystalline forms. This phenomenon (identical chemical structure but different crystalline structure) is referred to as polymorphism, and the species having different molecular structures are referred to as polymorphs.
Polymorphs of a particular organic pharmaceutical compound may have different physical properties, such as solubility and hygroscopicity, due to their distinct three-dimensional crystal structures. However, it is generally not possible to predict whether a particular organic compound will form different crystalline forms, let alone predict the structure and properties of the crystalline forms themselves. The discovery of a new crystalline or polymorph form of a pharmaceutically useful compound may provide a new opportunity for improving the overall characteristics of a pharmaceutical product. It enlarges the repertoire of materials that a formulation scientist has available for designing. It may be advantageous when this repertoire is enlarged by the discovery of new polymorphs of a useful compound.
Chinese Patent Publication No. CN1305860C discloses the structure of Icotinib (free base), on page 29, Example 15, Compound 23, and WO 2010/003313 disclosed Icotinib hydrochloride and its new crystalline polymorphs.